Power supplies often utilize relays for switching on and off power provided to an output of the power supply and therefore to a load. Relays are used due to the low resistance and therefore power dissipation of the relay contacts as compared to alternative switching devices, such as solid state relays, that have significantly higher voltage drops across the closed switch. However, the mechanical relays often degrade, at least in part, due to harmful arcing across the relay contacts that result from the relay contacts being powered before and after the opening and closing. Arcing often occurs across the relay contacts during the closing of the contacts, but prior to the relay contacts making physical contact. Similarly, arcing often occurs across the relay contacts after the contacts have initially separated, but prior to the separation distance being sufficient to break the energy flow across the relay contacts. Such arcing can cause damage to the relay contacts such as pitting of the relay contacts and are the primary cause of relay breakdown. This arcing is well known to cause early failure of the relay contacts and the need for replacement of the relays.
Heretofore, attempts to reduce the harmful and damaging contact arcing and bounce have involved mechanical apparatus such as bias springs and cams, and various electronic circuits including solid state devices such as transistors. These typically have focused on reducing or eliminating all arcing across the relay contacts, both during the closing of the contacts and the opening of the contacts. Typically, these electronic circuits have included complex and expensive solid state components that sense or detect the presence of arcing across the relay contacts and reduce the power at the relay contacts, thereby reducing the energy available for arcing. For example, electronic circuits have been designed to sense the pending closure of the relay contacts and remove or redirect the power away from the switch contacts until the contacts have made physical contact. Circuits also have been developed that sense or operate to reduce or remove the power from the relay contacts immediately prior to and during the separation from each other. Other circuits have been designed that provides a solid state relay circuit in parallel with mechanical relay contacts that often use specialized control circuitry, a triac, and/or digital circuitry. Many of the attempts to eliminate arcing having attempted to suppress arcing at both the closing and opening of the relay contacts, as generally, heretofore, all contact arcing was considered to be harmful.
Each of these has had the objective of providing a more reliable power supply circuit by increasing the life of the relay contacts. However, each of these have required considerable incremental complexity and cost to the power supply implementation. Additionally, many of these solutions do not provide a well-defined optimal turn-on and turn-off of the semiconductor switch.